Adding App::import() tests for plugin datasources.

cake/tests/cases/libs/configure.test.php

@@ -487,6 +487,10 @@ class AppImportTest extends UnitTestCase {
 
 			$file = App::import('Model', 'NonExistingModel');
 			$this->assertFalse($file);
+
+			$file = App::import('Datasource', 'DboSource');
+			$this->assertTrue($file);
+			$this->assertTrue(class_exists('DboSource'));
 		}
 
 		App::build(array(
@@ -502,6 +506,10 @@ class AppImportTest extends UnitTestCase {
 		$this->assertTrue($result);
 		$this->assertTrue(class_exists('OtherHelperHelper'));
 
+		$result = App::import('Datasource', 'TestPlugin.TestSource');
+		$this->assertTrue($result);
+		$this->assertTrue(class_exists('TestSource'));
+
 		App::build();
 	}